1. Field of the Invention
The present invention relates to a machining program creation apparatus for a wire electrical discharge machine (EDM).
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2015-123537 discloses a machining path generator for keyway cutting for a wire electrical discharge machine. In a machining program creation apparatus for a wire electrical discharge machine, a machining shape and a machining position are designated in order to generate a machining path. For example, in the case where a keyway shape is formed, a keyway width and a keyway depth are designated as a machining shape, and the diameter of a circular hole already formed in an object to be machined and center coordinates of the circular hole are designated as a machining position. An operator generates a machining path using this machining program creation apparatus.
Then, the operator draws a machining path using a machining path drawing device in order to check whether or not the generated machining path is correct. The machining path drawing device draws figures such as a straight line and a circular arc in accordance with the machining path. At this time, the machining path drawing device makes a drawing in accordance with the machining path, and therefore does not draw figures not included in the machining path such as a figure of the circular hole already formed in the object to be machined.
After checked the machining path using the machining path drawing device, the operator sets an NC program corresponding to the machining path in the wire electrical discharge machine, and then starts a machining operation to machine the object to be machined.
FIG. 1 shows one example of an input screen of a machining path generator for keyway cutting in a wire electrical discharge machine.
The operator effects the following data input operation                Machining dimensions of a keyway are inputted to “keyway width (b)” and “keyway depth (t)”.        Provided an entrance of the keyway is desired to be chamfered, an appropriate dimension is inputted to “chamfer (c)”        The diameter of a circular hole already formed in an object to be machined is inputted to “hole diameter (d)”.        A center position (coordinate position on the wire EDM machine) of the circular hole is inputted to “center coordinates”.        
When a “program creation” button is pressed after the above-described pieces of data are inputted, a machining path (NC program) for keyway cutting such as shown in FIG. 2A is generated.
Then, the operator draws the generated machining path using a machining path drawing device. FIG. 3 shows an example in which the machining path (NC program) in FIG. 2A is drawn. The operator checks whether or not the machining path is correct with reference to figures drawn on the screen.
After checked the machining path, the operator sets the NC program checked through the drawing in the wire electrical discharge machine, and starts a machining operation to machine the object to be machined. As described previously, the operator confirms the machining path through the drawn figures. However, in the drawing shown in FIG. 3, the operator can check a machining shape 40 of the keyway, but cannot check where the keyway is machined in the circular hole of the object to be machined. If, for example, a figure (figure 41 of the circular hole of the object to be machined) such as shown in FIG. 4 is drawn, the operator can confirm the machining shape and the machining position of the keyway with respect to the circular hole.
Generally, a machining path drawing device is adapted to draw figures as specified by a machining path (NC program) on a screen of a display device thereof, and cannot draw a figure not included in the machining path (NC program). For example, in FIG. 4, since the figure of the circular hole of the object to be machined, which is not a machining path, cannot be drawn, the positional relationship between the circular hole already formed in the object to be machined and the keyway shape cannot be confirmed by drawing.
Specifically, the positional relationship between the already formed circular hole and the keyway cannot be confirmed in a drawing on the display screen of the display device provided in the machining path drawing device.
Accordingly, it is difficult for the operator to easily and simply check the machining position (where the keyway is machined in the circular hole of the object to be machined) of the keyway. Thus, there has been a problem that the keyway is machined at an incorrect position and that machining has to be performed again.